I'm not sure if this is just a quirk of Duolingo...
I was asked to choose えも plus じ. From a grammatical/etymological point of view it would be better with え plus もじ. Especially as a precursor to learning the kanji.
They do this a lot for Japanese (I can't speak on behalf of the other languages) and just to try and catch you out. Nothing to do with grammar etc, they're just making sure you're paying attention lol =P
An exercise before this asked me to match corresponding words and gave me two variations or ways of writing "ji" - じ and a character that looked like the "chi" character (ち) but with two strokes on the upper right... what is the difference between the two?